Rig time is a significant cost item in a drilling program. Thus, techniques that can be used to reduce trips into and out of the hole, particularly during the drilling process but throughout drilling completion or workover are always desirable. One such trip-saving technique involves the use of a drillpipe mounted packer. This packer can be used when the entire casing string is assembled to test the pressure integrity below the packer. Use of this technique allows isolation of areas of the wellbore containing shallow abnormally pressurized sand. Thus, in situations where testing of each casing shoe to ensure pressure integrity is required, a packer is run as part of the drilling bottomhole assembly.
Prior techniques required the removal of the drillbit and the insertion of a blanking device for the mudline well template to be picked up on the drillpipe and run down to the sea floor. A remotely operated vehicle (ROV) equipped with a camera was used to establish the position of the drillpipe relative to the well slot in the template. Once that position was established, a submersible drilling vessel was moved to position the drillpipe above the proper slot in the template and the drillpipe was lowered to engage the blanking device into the well slot. Once in position, the casing string and the shoe could be pressure tested for leak off. Once the shoe was successfully tested, the blanking device and the drillpipe were removed and pulled back to the surface. The drill bit was reinstalled and run back into position just above the well template. Again, the vessel had to be repositioned to allow the bottomhole assembly to be run into the proper well slot. Drilling ahead then proceeded at this point.
The addition of a packer on the bottomhole assembly for the drilling streamlines this procedure. However, when using this type of technique at the conclusion of the pressure test for the shoe, drilling needed to continue. This involved circulation through the drillstring, through the bit and back up the annulus. The inflatables previously used in this application on a drillstring bottomhole assembly were of the type having a sliding collar to accommodate the expansion of the inflatable element. Upon deflation, the movable collar on the inflatable was subject to forces induced by circulating fluids during the drilling operation. In addition, cuttings from drilling would also come up the annulus around this deflated packer. The forces generated by the circulating fluid during drilling and potentially further combined with mud or cuttings sticking to the inflatable element on the inflatable put substantial forces uphole on the inflatable element. This tended to push the sliding collar uphole and force the inflatable element outwardly. The forces could be so great as to make the now deflated packer act as a piston to virtually drive the drillpipe out of the wellbore. Thus what was needed was an effective technique to hold the slidable collar against the forces created due to the circulating fluid in the annulus. Due to the sometimes large sizes of such packers, i.e., in the order of 13 inches or greater, coil springs were ineffective to provide a sufficient resisting force to the hydraulically induced forces from circulation. Accordingly, the objective of the present invention is to employ hydraulic principals and pressure differentials so as to provide a hydraulic assist to the sliding collar in the now deflated packer to prevent it from swabbing uphole as fluid is circulated during drilling.